


Let Me Ruin You

by asterkiss



Category: Gravity Falls
Genre: Alternate Universe, Cannibalism, Demon Mabel Pines, F/M, Human Bill Cipher, Implied Sexual Content, Murder, Oneshot, Unhealthy Relationships
Language: English
Status: Completed
Published: 2018-05-26
Updated: 2018-05-26
Packaged: 2019-05-03 05:59:26
Rating: Mature
Warnings: Graphic Depictions Of Violence, Major Character Death
Chapters: 1
Words: 4,905
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/14562402
Author URL: https://archiveofourown.org/users/asterkiss/pseuds/asterkiss
Summary: “The name’s Shooting Star,” the demon replied in a voice sweet like sugar as she tugged him forward by the lapels of his jacket. “...But you can just call me the girl of your dreams.”She crushed her lips over his.And their deal was sealed.[A reverse-AU where Bill is human and the Pines Twins are demons.]





	Let Me Ruin You

**Author's Note:**

> Bill is a human. Mabel is a demon.
> 
> A lot of messed up stuff happens.

He was twenty two when he killed his first victim.

He hadn’t been prepared for the amount of euphoria that manifested in watching the man’s final moments of life fade away from his eyes—it was a pleasant surprise.

The victim had been his former college professor who had been easily tricked into visiting his flat where they would be alone. For a man with multiple PhD’s, he had been incredibly stupid when it came to reading peoples underlying motives.

As the pool of blood upon the floor grew larger, Bill brought out the worn and tattered book that had fallen into his possession. It contained nefarious spells and dark magic and his life, which had always felt empty and lacking, seemed to finally have meaning when this came into his hands.

One of the spells was a summoning type—said to call forth a demon of unmeasurable power.

It required an elaborate pentagram drawn in fresh blood with the five vital human organs placed at each point of the star beside a lit candle.

Stanford should consider himself lucky that he was able to contribute to such a critical event.

* * *

The summoning didn’t necessarily meet all his expectations.

A blinding light took over the basement, and when it receded, it was to the sight of a star-shaped object floating in the air above the center of the pentagram. It was shimmering and shining, iridescent colours dancing upon its surface in harmony. It opened one solitary eye in the center of its body, black limbs growing out of its shape like shoots.

He swallowed thickly but kept his ground, holding his head high. He’d done it. He’d summoned a demonic entity from the other world. The creature before him had surpassed the rise and fall of kingdoms, and seen humanity evolve over thousands of years.

The demon’s eye focused on him as it hovered in the air, and a heavy silence stretched out between them.

Then, it’s eye crinkled in amusement. “…Hubba, Hubba.”

Bill blinked. “What?”

It released a giggle, the colours upon its form shining brighter as it spoke in an alluring voice. “Why _hello_ there, handsome. What can I do for a cutie like you, hmm?”

Uh. He cleared his throat, straightening up and tightening his grip on the tome in his arms. “I... I summoned you here in order to strike a contract, demon.”

“Oooh?~”

“I request your ongoing assistance and help in my endeavors,” he said, reciting his practiced lines in a firm and strong tone. “In return I will gladly hand over my soul.” Such an intangible thing meant nothing to him, after all.

It seemed to observe him for a moment before giggling. “Alright, you got yourself a deal, cutie.” 

Well, that had been easy and straight-forward. He reached out a hand but the demon laughed again, wagging a finger. “Oh no, I don’t strike my deals with a handshake!”

He blinked. “Then… how do you do it?”

Even though it held no mouth he could have sworn it smirked. The star released a short chuckle and then in the blink of an eye, Bill found himself staring at a young woman dressed in shades of black and pink with high heels elevating her a few inches above him. Dark hair cascaded down the young woman’s back with a star pin holding back her bangs away from her face. It was her eyes however that kept his focus. Piercing silver like ice, they froze him in place as she regarded him with intense scrutiny.

He wondered what she saw.

(She did, in fact, see a handsome yet disheveled man stained with blood from a nearby corpse. He looked startled at her new appearance and reminded her of a young babe, adorable and with promise but still so much to learn.

—It had been a while since she took a human under her wing).

Red-painted lips stretched into a slow smile.

“The name’s Shooting Star,” she replied in a voice sweet like sugar as she tugged him forward by the lapels of his jacket. He stumbled and sent one of the organs—a liver—rolling across the floor with a tap of his shoe where it came to rest between her feet. The dancing shadows cast by the flickering candles gave her expression a dark edge as she gazed down at him.

“...But you can just call me the girl of your dreams.”

She crushed her lips over his.

And their deal was sealed.

* * *

His life had always been boring.

His mother had been a drug addict and he'd been taken from her at four years old and placed into care. A long string of foster families had followed but he'd always failed to connect with them. They were all hypocrites anyway. They took him in with promises of affection but the moment he didn't adhere to their perfect public image, they dropped him like trash in an alleyway. Throughout his entire childhood he'd only ever been surrounded by worthless idiots and morons.

Determined to rise above them all, Bill reinvented his image over his teenage years. He became an A-grade student known for his charisma, popularity and good looks. People flocked to him like flies and sought to bask in his superiority on the off chance it might reflect upon their own pathetic lives. They were so predictable and boring.

But even when he found himself graduating from college and accepting a management position for a finance corporation, he found it wasn't enough. The power he desired went far beyond positions of authority in such small corporations. He wanted the power to rule over entire business empires, spanning globally across the world until his name was known everywhere and by everyone.

Shooting Star was the key to unlocking such a dream.

When he had found the spellbook hidden away beneath a loose floorboard in a public library, it was as if life was finally offering him a break. He had been dubious of its validity at first, but Prof. Stanford Pines was somewhat of an expert in supernatural oddities and upon inviting the old man over to examine it, he'd been alarmed and firm in the belief it was real. 

_"This is a dangerous thing to exist, Bill. If it fell into the wrong hands, the consequences could be dire-!"_

The poor sod. He only proved to secure his own demise. The old guy never even saw the knife coming from behind, heh.

"So, you want to be a Big Fish," Mabel cooed when he eventually told her his wish. His lips curled at her placating attitude as if he was a child, but she only smiled. "Sure thing, I can help you with that, not a problem. Buuuut... that might take a while to accomplish and keeping a human form for such a prolonged time takes quite an amount of energy." She tapped a finger against her chin. "So, I'd like to ask for a favour in return~" Her smile turned coy, gaze hungry with an emotion he couldn't place. "I have a rather large appetite. Do you think you could help fulfill it for me, cutie?"

He arched an eyebrow. "...With what?"

Her expression turned sinister, teeth flashing in a grin and eyes glowing an eery shade of silver. 

"Cm'on, you're smart. Think back, what was it you offered to summon me?"

Oh.

* * *

He killed again.

It turned out he was rather adapt at such a thing. It was a hell of a stress reliever. And, to be honest, the sight of those final seconds in a persons eyes before death awakened something within him. Something forbidden. Something unexplainable.

He was addicted to that feeling.

And he needed to feel it again.

Luckily, his partner with intangible powers was all too happy to assist him.

You couldn’t be caught for murder if they didn’t believe in the supernatural powers that made it possible.

They were a deadly and dangerous duo.

* * *

A few months into his killings he began carving encrypted words into his victims skin that when solved, would hint toward the location of the next body dump. Bill had always been rather fun of puzzles so leaving phrases for the authorities was amusing—he’d always had a particular fondness for the Caesar cipher.

It also meant they knew every victim belonged to one sole killer, even when spread across countless countries.

The pandominum it created within the public was like music to his ears.

* * *

Within a year he had control over multiple stock markets and was making more money than he knew what to do with. He purchased multiple corporations and remade them in his own image, steadily branching out his power whilst the world watched his steep ascent into the top 1% with awe. He was painted as a charming entrepreneur who had it all. Anything he wished for, he was granted.

It was amusing just how easy it was to climb to power. 

* * *

He bought a penthouse apartment for a few million that barely made a dent in his finances. 

His partner sighed happily as she floated on the surface of the pool, limbs outstretched so she resembled a star. She certainly enjoyed the luxuries his new life came with, indulging in them with bliss. She turned her head after a while and looked in his direction as he laid by the poolside on a chair, fully clothed with a laptop before him as as he planned which business to overtake and blend into his rising empire next. (Nothing was impossible when you had a demon companion).

"You're not coming in?" 

"Later." There was a trading corporation based in Bei Jing that looked promising. If he killed the current CEO they'd be in a panic and ripe for the picking.

The screen before him suddenly vanished as a pair of slim hands closed the laptop and placed it aside. He raised his head to find a pair of silver eyes boring into him, accompanied with a sly smile. She leaned over him and poked a solitary finger against his chest. "You need to learn how to take a break, Mister."

Any response he could give was stolen away when she grabbed him by the arms and yanked him out of the chair with astonishing strength that reminded him she was in fact a demon in disguise. A second later he was plummeting into the water, fully clothed, as she laughed loudly in triumph from the poolside.

When he surfaced to spit out water, he shot her a look as water dripped from his hair. The phone within his jacket pocket was definitely dead but what did he care, he could buy hundreds of replacements.

Bill wasn't really mad though, and after a moment his expression morphed into mischief. She was so caught in her laughter, she didn't notice him drawing closer until it was too late. Grabbing her by the ankles, he pulled her down into the pool to join him. 

The pair, comprised of a deadly serial-killer and an omnipotent demon, laughed as they indulged in a moment of harmless play.

It was the first time they had fun together which didn't involve murder.

* * *

One night he laid on the sofa with his head upon her lap as she weaved fingers through his hair. She was the only one he would grant such permission to. Her soft touch lulled him to sleep and he dreamed of distant voices in conversation.

“So this is where you've been,” a male voice murmured. “I was wondering why you’d been AWOL for a while and now I know why. Another human? Really?”

"Oh, don't be like that, Dip-Dot. I’m just having a bit of fun.”

“Your kind of fun always ends up causing a huge mess. Do I need to remind you of the last time you had a pet?”

“That wasn’t my fault. He was the one who declared war."

"You—"

“What do you want, Dipper? I’m busy.”

“With this human?” A scoff. “You know as well as I do that you’ll grow bored of your newest plaything soon enough. You always do.”

“What I do and who I interact with is none of your concern.”

“I suppose not.” A pause. “Just don’t come whining to me when your interest sways and your toy becomes bothersome.”

Silence.

When Bill later awoke, he was alone.

* * *

Usually, Bill removed the organs from his kills and presented them to her like a gift which she accepted with a peck on his cheek before taking them elsewhere.

But one day he walked in on her eating within the center of the kitchen, seated upon the island counter.

The first time Bill witnessed her biting into raw flesh, blood staining her hands and mouth, he felt his heart skip a beat. The young woman saw him watching and smirked, keeping his gaze as she chomped down onto the still-fresh organ, tearing a chunk of flesh off and swallowing it whole.

She raised red-stained fingers to her lips and licked them clean, still holding his gaze and almost taunting him to come closer.

What he felt was a mix of fear, admiration and arousal.

For the first time in his life, Bill knew what it felt like to experience attraction to someone out of your league.

* * *

"Make sure you're free on Saturday," he stated, not even looking her way.

"Hm? Why?"

"We're going out for dinner." 

They'd often dined out together over the past few years of their partnership but this time was different. His intentions behind it weren't the same. She must have been able to tell because her lips quirked up into a smile as she regarded him, cupping her face in her hands.

"Oh my gosh, are you asking me out on a date?" With her eyes alight and cheeks flushed, she looked like an ordinary young woman squealing in excitement compared to an ancient being of demonic origins. The only thing that gave her away was the barely contained amusement within her eyes.

"Is that a problem?" He tried to sound casual, but he couldn't help the inclined rate of his heartbeat as he waited her response.

"Mhhm, I guess not."

He returned her smile, rejuvenated with a new energy as he slammed down the protective visor of his helmet once more and revved up the chainsaw in his hands again. His gleeful grin remained as he brought the saw toward the gagged and struggling man strapped to the wall.

* * *

~~~~“How many humans have been your partner before?”

She gave a derisive snort. “As if I could recall.”

“Try.”

She looked at him, her usual smile vanishing as she regarded his expression before speaking calmly. “Does a spider recall every bug it’s ever caught in its net?”

He looked away with his lips twisted into a scowl and left the room. 

She was simply using him.

But even if he wanted to, he could never leave her web.

He was in too deep.

* * *

A few months into his official 'courting', he offered to make her dinner.

He placed another chunk of liver upon the plate beside his chopping board, sleeves rolled back to his elbows as he partook in such culinary arts. This particular ingredient belonged to some dim-witted European Prince. When it came down to it, royalty or not, everyone looked the same on the inside regardless of wealth.

A pair of arms entwined around his torso from behind and he felt her hair tickle his cheek as she peered over his shoulder. Placing one final piece on the plate which he then smothered in a sauce of his own making, Bill twisted around and displayed it to her.

“Dinner is served."

She raised an eyebrow as she regarded the contents curiously. “What's this?”

“Liver served in bordelaise sauce with dried and fresh figs on the side.” He smirked. “A gourmet meal to fit the pompous nimwit who contributed to it.”

She plucked one of the pieces of meat between two fingers, eyeing it for a moment before plopping it into her mouth in one swift movement. Her eyes fluttered close as she chewed and Bill found himself fixated on her tongue as it flicked out to catch a stray drop of sauce.

His grip on the plate tightened.

She chuckled.

He snapped his gaze up to find her gazing at him through half-lidded eyes full of amusement. She took a step forward, face hovering in close proximity to his own.

“Tell me Bill, have you ever wondered what a human tasted like?”

“What?” His pulse quickened.

She was the one smirking now, and suddenly she was holding another piece of liver against his closed lips.

“Say ‘aah’~”

His heart skipped a beat. Killing was one thing but cannibalism? He wasn’t so sure.

...But how could he say no to her?

He slowly parted his lips and the raw piece of flesh was plunged into his mouth. He allowed it to settle upon his tongue without action for a moment.

She was watching him intensely.

Slowly—very slowly—he moved his teeth and chewed into the rubbery piece that had once been part of another humans body. It was like eating hard jelly and the overwhelming taste of flesh was nauseating even with the sauce.

Somehow, he was able to swallow it all.

A giggle and she was taking the plate out of his hands and placing it on the counter before looping her arms around his neck and pressing up against him.

“How does it taste?”

“...Like blood."

She laughed. Moving one hand to take another piece, she tilted her head back to drop it into her mouth as she hummed in approval. After a few moments she crushed her lips against his and Bill stumbled back in surprise before regaining himself and grabbing onto her tightly.

Then she parted his lips and the sensation of chewed up flesh entered his mouth.

It should have disgusted him.

But the taste of her lips which he’d fantasied over countless times overrided anything else.

The rest of the meal was sent scattering to the floor along with their clothes as she straddled him on the counter-top and eyed him hungrily.

Maybe he could gain a taste for flesh after all.

* * *

“Do you have a name?”

“Well duh, I have many names.”

He looked down at the crown of her head as she laid across his form in bed, one of her fingers tracing symbols he couldn’t recognise along his skin. Her touch was burning.

“What was the first name you went by?” he asked.

Her finger stopped.

She raised her head, silver eyes piercing into his own as she scanned his face for… something.

Eventually she closed her eyes and dropped her head back down onto his chest, appearing to have a fondness for listening to his heart. 

“...Mabel,” she whispered, voice soft. “It was Mabel.”

* * *

Their partnership continued.

They killed, they feasted, they tangled together in the sheets.

He killed royalty, politicians, celebrities and renowned artists.  

Five years after their deal, and he finally acclaimed the title 'Richest Person in the World' with a net-worth of $120 billion.

He also happened to have the highest count of any serial killer in recorded history, with his latest victim clocking it at #141.

It was hard to say which achievement of the two he was most proud of.

* * *

Another night, another victim.

He was rather proud of his method of killing on this occasion. By the time he was finished there was scarcely an inch of flooring or wall within the room that wasn’t splattered with red.

He turned towards his partner—his Shooting Star—with an anticipating grin.

But she wasn’t paying attention.

Staring down at her feet, seemingly lost in thought, it wasn’t until he cleared his throat that she lifted her head in surprise. Mabel took in the sight of the body and then him.

She gave him a smile but it felt false and the only emotion it invoked in him was dread.

His insides twisted.

* * *

She stopped attending his killings.

She stopped sending him coy smiles.

She was pulling away and he scrambled to find some way to regain her attention, to be the object of her affection.

* * *

"Marry me."

"Say what?"

They were fine dining upon a balcony in France, with the Paris skyline as their backdrop. He held out the jewelry box across the table towards her, a ring worth more than most peoples lives on display. He saw her eyes glow in delight at the sight of it since she did love sparkly things.

But then she raised her gaze towards him and gave a small smile. "I can't."

He scowled, insides twisting. "Why not?" 

"Well...." She twirled a lock of hair as she observed the ring between them, leaning back in her chair. "Marriage is the legal union of two individuals being recognized as equal partners in a personal relationship."

"And?"

She met his eyes again, and suddenly he felt a heavy presence crushing down upon him. It was smothering, and he gripped the table with both hands so tightly he almost broke the wood. Meanwhile, Mabel sat unaffected and continued to watch him with a pitying smile.

"We're **not** equal."

* * *

Their partnership became strained after that.

Months later they attended a party with other celebrities and CEOs. He lost sight of her soon after.

Later, he spotted her cosied up with a foreign Chairman as she giggled and brushed her hand over the morons thigh.

He left the party in a blind rage.

Bill was driving through a seedy part of the city when he caught sight of a woman smoking on the sidewalk. With brown hair and icy blue eyes, if he didn't look too hard, she could almost resemble Mabel.

She eventually caught him watching her from his car and raised an eyebrow. He smirked and wound down the window as she approached and leaned forward to eye him, likely noting his expensive car and attire.

"It's a hundred per half hour, kid."

He held out his hand with a large wad of cash on display. The way her eyes widened was almost comical. "How 'bout this much?"

"...For that amount, you can do anything you want to me."

He grinned, flashing his teeth.

"Good to know."

* * *

Two hours later and he sat upright in bed in one of his many apartments, the woman laid beside him with dark bruises surrounding her throat like a collar as she stared at the ceiling unblinking.

It was the first time he'd murdered for his own sake.

Mabel came in hours later when he was seated watching the news. She threw her bag at his head, glaring as it bounced off him. "Hey, you could have let me know if you were leaving!"

"I didn't want to interrupt your fun with your new boy toy."

Her expression sobered up. She parted her lips to reply but then paused, her nose crinkling as she sniffed the air. A moment later she was spinning around to look in the direction of his bedroom before returning her attention his way. "You killed someone?"

He said nothing.

"They smell atrocious. You know I can't stand the taste of humans who are diseased. I mean, jeez, did you pick them up off some street corner or something?"

"Yup."

Silence followed his lackadaisical comment and he made a point of keeping his gaze fixated on the television screen across from him, not once looking in her direction.

Eventually, after a few minutes, he turned his head.

She was gone.

* * *

"I told you so."

"Shut up, Dipper."

"I'm just saying—"

"I _know_ what you're saying, so quit being so smug."

A pause."If you want, I can arrange to kill him. That way, you can collect his soul and move on. Consider it a sibling favour."

She chewed her bottom lip, saying nothing.

"Cm'on, it's not like you actually like the human. He's just a plaything."

"...It's fine, I'll deal with this myself."

"Suit yourself. You sure have a way of picking them, Mabel."

A sigh. "I do, don't I?"

* * *

After several weeks she sensed him summoning her, so she obliged and appeared. She found herself stood within a pristine white room that she recognised. It was one of his many sound-proof killing rooms.

She sensed movement behind her and turned.

"Bill—"

His lips crushed against her and she almost lost her balance but he wrapped his arms around her, holding her close. His kisses were desperate and after a moment of deliberation she decided to indulge him, articles of clothing being discarded aside soon after.

She was straddling him and feeling rather flushed when there was a flash of silver.

The brunette stared down at him in stunned silence as he lay beneath her with a dark expression, knife in hand. A few seconds passed before blood spurted out from her cut throat, showering him in a red rain.

Her body dropped and he caught her.

"I guess demons can bleed," he remarked dryly.

* * *

She didn't die. Of course.

Her human form was a simple physical illusion. She bled out in his arms and then, an hour later, they were talking upstairs.

"So, like, is this your new kink?" she asked, raising an eyebrow as she sat at his kitchen table. They were both still stained in blood, although the injury on her neck had since vanished. "You fuck girls and then kill them?"

"I only fucked and killed girls who reminded me of you."

She smiled. "...You're lucky I'm a demon since I'm pretty sure any normal human would be creeped out by that, dude." 

“I’ve lost you, haven’t I?” 

Her smile dropped.

Bill stared at her with resignation and bitterness. It was over. She’d grown bored with him. The way she avoided his gaze following his question was all the proof he needed.

“I love you.”

She released what he thought was a snort, and rolled her eyes. “Yeah right, you don’t love me.”

“I do.”

She snapped her head back around towards him, her expression sharp and all traces of teasing gone. “You’re feelings stem from obsession. You _want_ me Bill, you don’t love me. Just like how you want the best of everything and.... well, let's face it, I _am_ the best." She gave a brief haughty smile as she threw her hair over her shoulder before continuing. "Either way, every human I deal with is the same. And look, it’s fun in the beginning—flattering, even—but you’re forgetting something here.”

“What is that?”

She was suddenly leaning across the table, nose to nose with him.

“I’m a demon,” she breathed, eyes flashing alight and in that moment he felt like he really was eye-to-eye with a demon of ancient times. Her hand pressed over his chest where his heart lay beating and when her fingers curled, nails biting into his skin, her touch seemed to physically scorch him. “If you give your heart to me, I’ll just eat it up.”

He grit his teeth against the pain of burning flesh.

“Maybe that’s what I want.”

She blinked in surprise before giving a soft smile.

And then she kissed him and his mind went dizzy.

The next morning he woke up in bed alone.

* * *

Two days later he walked into a police station and admitted to killing 157 people, with photographic evidence of many of their bodies acting as undeniable proof.

The world was thrown into chaos as it reeled from his confessions. His name covered every single news outlet in every country. His name would go down in the history books for centuries following his death.

He'd always dreamed of this kind of fame. Now, he finally had it.

One day whilst laying in his jail cell, he awoke to a pair of eyes watching him from above. She stood over his bed with an unreadable expression.

“Hey, Shooting Star.”

"This is how you want it to end?" she asked, looking almost disappointed. Though why, he had no idea.

"Aw, going soft on me now?" he mocked, lips quirking.

Mabel frowned but said nothing. He would, of course, be given the death penalty in his current situation. It was guaranteed even with his vast wealth and power.

"...See you later, Bill."

She vanished and he was left alone. 

But he knew he'd see her again.

* * *

When he was eventually given the death penalty, she appeared before him the night before his appointment in the darkness. 

"Long time no see," he quipped as she leaned over him, seated on the edge of his bed.

Her face filled his vision, those ice-like eyes gazing into his own one last time as she pressed her lips chastely against his, her hand against his chest.

“...You were one of my favourites."

Then there was pain and he blacked out.

* * *

“What on earth happened!?”

“I-I dunno! We just- we came by and he was just dead like that! His heart it- it was carved right out-!”

“God, there’s so much blood.. Get the entire building on lock-down!”

Sirens wailed as Bill lay with glassy unblinking eyes, a smile stuck on his face.

Elsewhere, a young woman walked down a street, discreetly raising a finger to wipe blood from her chin before she vanished from existance.

It was the best meal she'd had in a lifetime.

**Author's Note:**

> I honestly didn’t intend for this to get as dark as it did... I swear. But when you're dealing with a sociopathtic serial killer and a cannabilistic demon, things spiral out of control fast. 
> 
> But after this I'm done writing dark oneshots for now. The next one I'm working on *does* end happily and is a lot more light hearted—I promise!!
> 
> Inspirations:  
> [\- The song 'Partners in Crime' by Set It Off;](https://www.youtube.com/watch?v=VwpudWRx7eg)  
> [\- This fanart; and](http://fuckyeahmabill.tumblr.com/post/144466283545)  
> \- The tone for this story was loosely inspired by a MaBill fanfic on fanfiction.net called ['Toxic Blood.'](https://www.fanfiction.net/s/11568630/1/Toxic-Blood) If you enjoyed the tone of this story, you should check that one out too!


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